Four whole-rock samples of Nanhuatang granite-porphyry in Wudang orogen give a Rb-Sr isochron age of (237±19) Ma, which represents the formation age of the granite-porphyry body. This discovery has not only filled up the gap in Indosinian magmatic record in Wudang orogen but also provided the direct evidence for studying and determining the heat source of deposits in Indosinian period in Wudang region.